The expression of the p53 and RB tumor suppressor genes in seven human hepatocellular carcinoma and hepatoblastoma cell lines was evaluated by northern and western blot and immunohistochemistry. The expression of p53 was abnormal as indicated by the absence of detectable p53 RNA or the overexpression of p53 protein in five of the seven cell lines; the overexpressed p53 protein appeared to be the product of a mutant p53 gene. Although RB RNA was detectable in all seven cell lines, RB protein was undetectable in three of the cell lines but was detectable in the other four. The RB tumor suppressor gene product was examined by immunohistochemistry in frozen sections from 14 human HCCs from China. Hepatitis B surface antigen (HBsAg) was detectable in adjacent nontumorous liver from all 14 HCC patients. RB protein was absent from HCC cells of 3/14 (21%) HCCs. Abnormalities of the RB gene were analyzed within exons 12-23 by single- strand conformation polymorphism (SSCP) using five overlapping segments of 129 to 337 nucleotides each. Five cell lines derived from human HCCs were studied. (All mutations or deletions of the RB gene reported in other human cancers have encompassed portions of exons 12-23. Deletions in the RB cDNA were found in exons 17-21 in two of the cell lines, and in exons 20-21 in the third cell line. The exons examined were normal in the remaining cell lines. p53 was examined by immunohistochemistry in tissues of liver tumors that are thought to be possible precursors of HCC, as well as HCCs, from Hungarian patients. Mutant p53 was detected in 8 of 16 HCCs and in none of 23 benign liver tumors.